1. Field of the Invention
The present invention relates to a pneumatic wrench, and more particularly to a pneumatic wrench having a reinforced structural strength to withstand a larger torque.
2. Description of the Related Art
A conventional pneumatic wrench in accordance with the prior art shown in FIGS. 7–11 comprises a pneumatic motor (not shown), a striking mechanism 10, and a drive shaft 20. The drive shaft 20 is mounted on a socket (not shown), the striking mechanism 10 is mounted on the drive shaft 20, and the pneumatic motor is mounted on the striking mechanism 10 so that the striking mechanism 10 is mounted between the pneumatic motor and the drive shaft 20. Thus, the striking mechanism 10 is driven by the pneumatic motor to rotate in the normal direction and the reverse direction to drive the drive shaft 20 to rotate, so that the drive shaft 20 is driven to rotate the socket mounted on the drive shaft 20 so as to drive and rotate a screw member, such as a bolt, nut or the like.
The striking mechanism 10 includes a cylindrical support seat 11 having a closed first end face and an open second end face, a cam 13 rotatably mounted on the first end face of the support seat 11 and engaged with and rotated by the pneumatic motor, a cover 12 mounted on the second end face of the support seat 11, and a hammer 16 rotatably mounted in the support seat 11 and engaged with the cam 13 so that the hammer 16 is driven by the cam 13 to rotate in the support seat 11. The cam 13 has a periphery formed with an engaging recess 14. The hammer 16 has a first end formed with a protruding engaging portion 17 engaged in and driven by the engaging recess 14 of the cam 13 so that the hammer 16 is driven by the cam 13 to rotate in the support seat 11. The first end of the hammer 16 is formed with a first pivot shaft 18 pivotally mounted in the first end face of the support seat 11. The hammer 16 has a second end formed with a second pivot shaft 180 pivotally mounted in the second end face of the support seat 11. The second end face of the support seat 11 has a periphery formed with a pivot hole 110 for mounting the second pivot shaft 180 of the hammer 16. The drive shaft 20 has a first end formed with an engaging portion 25 engaged with the hammer 16 and a second end formed with a mounting section 22 for mounting the socket. The engaging portion 25 of the drive shaft 20 is formed with a driven groove 26 engaged with and driven by the hammer 16 so as to produce a striking effect on the drive shaft 20 by rotation of the hammer 16.
In operation, after the compressed air enters the pneumatic motor, the pneumatic motor is operated to rotate the cam 13 which engages the hammer 16 so that the hammer 16 is driven by the cam 13 to pivot in the support seat 11. Thus, the hammer 16 is pivoted to strike the drive shaft 20, and the hammer 16 strikes the drive shaft 20 once when the hammer 16 is rotated through a circle, so that the drive shaft 20 is driven to rotate the socket mounted on the mounting portion 22 of the drive shaft 20 so as to drive and rotate a screw member, such as a bolt, nut or the like.
However, the hammer 16 is substantially arc-shaped so that most of the stress of the hammer 16 is concentrated on the two opposite sides 160 of the hammer 16 during operation of the hammer 16, so that the hammer 16 is easily distorted or broken during a long-term utilization, thereby decreasing the lifetime of the hammer 16.